The use of dense wavelength division multiplexing, DWDM, technology in mobile backhaul systems is required to cope with an increasing volume of traffic, especially when it is mixed with wire line traffic in a convergence scenario. Mobile Backhaul, MBH, is a multi-purpose transport network that connects base stations to network controllers within a geographical coverage area. MBH transport function is crucial in mobile networks and if not well planned and structured it can pose a real bottleneck in a radio access network, RAN. MBH is conventionally divided in two sections: low RAN, LRAN, the cell site access section, and high RAN, HRAN, the part of the network that collects, aggregates, and concentrates traffic from LRAN for connecting to the radio controllers. LRAN can be based on microwave, copper of optical fibre links arranged in point to point or ring topologies. HRAN is commonly based on optical fibre links arranged in a ring topology. However meshed HRANs can be used to increase the level of resource sharing and to improve the level of resiliency (to withstand multiple failures).
The introduction of differentiated broadband services requiring low latency, the increase of the traffic load, the convergence of the mobile and fixed infrastructures, the need for site consolidation, and energy saving are all reasons calling for the introduction of an optical solution in radio access and backhaul networks, where packet processing is implemented at the access and metro edge of the network and intermediate channel add-drop and ring interconnection is performed at the physical layer in the optical domain. However, conventional optical technologies and node architectures are not suitable for MBH due to their cost and complexity. E. J. Klein et al “Densely integrated microring resonator based photonic devices for use in access networks”, Optics Express, pages 10346-10355, vol. 15, no. 16, 6 Aug. 2007, reports two reconfigurable optical add-drop multiplexers and a 1×4×4 reconfigurable wavelength-router based on thermally tuneable vertically coupled micro-ring resonators fabricated in Si3N4/SiO2 for use in access networks.